It is known that the pre-junctional functions of the sympathetic nervous system are reciprocal and mutually inhibitory with those of the parasympathetic system. In addition, these regulatory reciprocal mechanisms act to modulate the adenylate cyclase-phosphodiesterase system which, in turn, modulates the release of chemical mediators of the antigen-antibody reaction. Since the experimental data from several laboratories suggest that a dysfunction of the sympathetic nervous system exists in bronchial asthma, it is probable that this delicate and crucial balancing has been disrupted. We are studying in healthy, anaphylactic and antigen-sensitized guinea pig lungs the interrelationships between the two branches of the nervous system and the effects of various chemical mediators on their inter-relationships and on the adenylate cyclase-phosphodiesterase system.